Officers are examining whether fog or smoke from a nearby bonfire and fireworks event may have been a factor.

BBC: M5 crash: Retired couple from Newport among victims

Tuzla is a dismal compound of valley fog and wood smoke -- and its people are not in the mood to celebrate the peace agreement.

CNN: Bosnian city gets ready for NATO peacekeepers

The image is grainy, but good enough to be able to fly at very low level at night, although rain, fog, or smoke adversely affect it.

BBC: News | In Depth | Military Fact Files

Rox said its "highly sophisticated" new smoke cloud system released a heavy fog which reduced visibility when activated.

BBC: Rox in George Street in Edinburgh

Weather forecasts called for dense fog Wednesday morning, and McGlamery said motorists reported smoke across the highway.

NPR: Authorities: 4 Dead In Fiery Highway Crash In Ga.